Rheostat



(No Model.)

C. WILLMS.

RHBOSTAT.

No. 475,529. Patented May Z4, 1892.

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, jaag/zh' ww WMM mw 2mm m UNITED STATES 'PATENT FFICE.

CHARLES VILLMS, OF BALTIMORE, MARYLAND.

RH EOSTAT.

SPECIFICATION forming part of Letters Patent No. 475,529, dated May 24,1892.

Application filed January 14, 1892. Serial No. 418,037. (No model.)

-To @ZZ whom, t may concern:

Be it known that l, CHARLES WLLMs, a citizen of the United States,residing at Baltimore, in the State of Maryland, have invented certainnewand useful Improvements in Rheestats, fully described and representedin the following specification and the accompanying drawings, forming apart of the same.

The object of the-present invention is to improve the construction ofrheostats or current-regulators; and especially to provide an improvedrheostat of that class employing a plastic resistance material orcompound forming a path for the current between the terminals and aseries of conductors with any one of which the other terminal is broughtin contact, according to the resistance desired.

As a full understanding of my invention can best be given by a detaileddescription of a rheostat embodying the same, such description will nowbe given in connection with the accompanying drawings, and the featuresforming my invention specifically pointed out in the claims.

In the drawings, Figure 1 is a plan View of a convenient form ofrheostat embodying my invention. Fig. 2 is a reversed plan of the same.Fig. 3 is a side elevation. Fig. 4 is a section on the line 4 4 of Figs.l and 2. Fig. 5 is a reversed plan of a modified form of rheostat withthe bottom plate removed. Fig. 6 is a section on the line 6 G of Fig. 5.

Referring now especially to Figs. l to 4, A is a block of insulatingmaterial, preferably rubber, and a b the binding-posts, mounted thereonand formingthe terminals. The binding-posts a b pass through the block Aand connect, respectively, with metallic cont-actplates c d, secured tothe under side of the block, the plate c forming a contact-plate fromwhich the current passes through the insulating material, and the plateCZ connecting by means of a stud c, extending through the middle of theblock, with a contact-arm f, moving in the arc of a circle over the topof the block and actuated by means of an insulating inger-piece g,connected to the stud c and arm CZ by a cross-pin, as shown, or in anyother suitable manner. The contact-arm j' moves over and makes contactwith a series of conductors consisting in the form shown of pins 7l,preferably level with the top of the block and extending through theblock so as to be level with or project from the under side of the same.While these conductors are shown as pins and as of the same size on bothsides of the block, it will be understood that they may be of any othersuitable construction and that the area of their surface on the underside of the block may be increased in any suitable manner if a widerconducting-surface in contact with the resistance material be desired.rlhe contact-arm f may connect directly With the conductors h; butcontact is preferably made by a pivoted block 7c, carried by the arm fand having a flat surface on the under side, so as to form an extendedcontact-surface, the block 7c beingpreferably of sufficient width so asto make contact with two of the conductors simultaneously. The danger ofbreakage of the circuit through failure of the armfto make contact withthe conductors where only one is engaged is thus avoided, and thepivoted connection of the block 7o With the arm f permits the block toadapt itself to any unevenness and secures a good contact. Thebinding-post a may make contact directly with the plate c; but for thepurpose of securing a large outlet and full conduction for the current Ipreferably connect the binding-post b with a wire Z, which is bentwithin a recess in the under side of the block, so as to make contactwith a large part of the inner surface of the plate d, which is securedto the block so as to cover the recess, space thus bein g afforded forpacking` the resistance material about the wire and the inner side ofthe plate. The conductors 7L extend about the block in the are of acircle, which is shown in the drawings as nearly complete; but it willbe understood that the length of the are may be varied as desired andmay be any portion of a circle and that the circular form is notessential, but is adopted simply on account of con venicnce in makingcontact with a single point through an arm swinging in the arc of acircle. The conductors h on the under side of the block are covered tothe desired thickness with insulating material, which is applied so thatthe path of resistance material is of substantially the same width asthe conductors on the under side of the block throughout the greaterportion of the path. For the purpose, however, of securing a very largeresistance at the starting-point the resistance IOO material ispreferably applied so as to form a very narrow path for a small distancefrom the starting-point. For the purpose of securing a large outlet forthe current at the opposite end the width of the path of resistancematerial at this end is preferably made as great as possible, extendingthe full length of the plate c, and for the purpose of securing thegreatest possible conductivity between the resistance material and thebinding-post a the resistance material preferably entirely covers theplate c on the under side of the block and is packed into the recesscontaining the wire l, so as to completely surround the wire and theside of the plate c inside the recess.

It will be understood that the resistance material may be of anysuitable material capable of being applied to theunder side of theblock, so as to form a path for the current between the conductors h. Amixture of finely-divided carbon, in the form of plum bago or lamp-blackand glue or other suitable non-conductive material, is generally used;but any other suitable compound or mixture may be used. The thicknessvot' the resistance material upon the conductors may be varied as desiredin accordance with the amount of current for use with which the rheostatis intended. It a verylight current is to be used, only a thin layer ofresistance material is required, and this will be increased with thequantity of current the rheostat is designed to transmit.

In the construction thus far described I have shown only one series ofconductors. It is evident, however, that two or more series may be used,and in some cases this will be preferable. In Figs. 5 and G I have showna construction in which three series of conductors are employed. By theuse of two or more series of conductors and two or more paths ofresistance material I am able to provide a small rheostat, which may beused with very large currents without danger of burning out thecontacts, and, moreover, I secure greater certainty that the circuitwill not be accidentally broken through failure of contact of the arm fwith one of the conductors or of one of the conductors with theresistance material, the contact-arm f in this case being provided withblocks 7a, moving overthe three series of conductors, so that in case ofthe failure of one block to make good contact between the arm fand itsline of conductors this result will be accomplished by the otherconductors. In these iigures, also, I have shown the block as provided.on the under side with grooves for the reception of the resistancematerial outside the conductors, and this feature forms apart of myinvention. By the use of these grooves the resistance material may bemore rapidly applied, so as to form a path of the desired width, and thematerial is more closely held in place and less liable to flake oft orto be accidentally removed. I am thus enabled, also, to applyconstruction shown, but that the features forming my invention may beapplied to rheostats of other forms.

What I claim ism l. In a rheostat, the combination, with aIsupporting-block provided with grooves, of a conducting-plate withwhich one conductor of the circuit connects, one or more series ofconductors arranged in said grooves and extending through the block, amovable contact-piece with which the other conductor of the circuitconnects and which is adapted to form contact with any one of eachseries of conductors and resistance material applied to the conductorswithin the grooves and forming a path or paths for the current betweenthe conducting-plate and successive conductors, substantially asdescribed.

2. The combination, with insulating-block .A, of conducting-plate c onone side of the block, with which one conductor of the circuit connects,contact-piece f on the other side of the block, mounted to move inthearc of a circle and with which the other conductor of the circuitconnects, one or more series of conducting-pins 7L, extending throughthe block and arranged on the circle traversed by the contact-arm f toform contact therewith, and resistance material on the same side of theblock as conducting-piece c and forming a path or paths for the currentlof substantially the same width as the conducting-pins 7i,substantially as described.

3. The combination, with insulating-block y A, having grooves on oneface, of conductingpiece c on one side of the block, with which oneconductor of the circuit connects, contact-piecef on the other side ofthe block mounted to move in the arc of a circle and with which theother conductor ofthe circuit connects, one or more series ofconductingpins 7i, extending through the block and arranged on thecircle traversed by the contactarm f to form contact therewith, andresist- .ance material applied within the grooves on the same side ofthev block as conducting- `piece c and forming a path or paths for thecurrent, substantially as described.

In testimony whereof I have hereunto set my hand in the presence of twosubscribing witnesses.

Cll. WILLMS.

Witnesses:

J AMES J. WARRINGTON, WM. H. JONES,

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